Superconducting magnets are needed for most high field EPR spectrometers. Superconducting magnets are designed to keep the magnetic field at constant value, not to sweep. Wide-range scanning of these magnets presents a challenge in accurate magnetic field measurement and control. NMR and Hall-effect Gaussmeters as well as high-speed current transducer have been used, and their accuracy compared, to measure field values. Hysteresis-like behavior has been measured in the field sweep, and this has been studied as a function of magnet history. The non-linear hysteresis-like behavior is repeatable thus allowing the use of the current-feedback as one of the mechanisms in controlling magnet field. Custom-fabricated Hall devices for field measurements/feedback control are being tested.